This invention relates generally to transfer circuits and particularly to a system for applying grey scale codes to the pixels of a display device.
Many display devices, such as liquid crystal displays, are composed of a matrix of active elements, or pixels, arranged vertically in columns and horizontally in rows. The data to be displayed are applied as drive voltages to data lines which are individually associated with each column of active elements. The rows of active elements are sequentially scanned and the individual active elements within the activated row are illuminated to grey scale levels in accordance with the levels of the drive voltages applied to the various columns. Typically in a display device the grey scale levels are received as an analog video signal. The analog signal is applied to an analog-to-digital converter (A/D) to place the brightness signals in digital format. A digital code is thus provided for the brightness level for each of the columns of active elements within the display device. Liquid crystal displays for color television, or high quality display devices, typically include 250,000 to 750,000 liquid crystals. Typically, the display includes 1,440 vertical columns and approximately 175 to 520 horizontal rows, depending upon the size of the display. Accordingly, actuating each column of active elements with an individual brightness signal requires 1,440 output lines from the digital circuitry. Providing 1,440 output lines on a standard liquid crystal matrix is a formidable task because of physical constraints. Also, the incoming data are stored in shift registers prior to being transferred to the display matrix. The physical constraints also make it very difficult to provide 1440 separate shift registers which are serially unloaded. For these reasons there is a need for a system for rapidly applying a large number of digital grey scale codes to the columns of active elements of a display device. The present invention fulfills this need.